1. Field of the Invention
The present invention relates to an image-bearing member protecting agent, a protective layer forming device, a process cartridge using the protective layer forming device, and an image forming apparatus using the process cartridge. More specifically, the present invention relates to a protective layer on the surface of a latent image bearing member to be uniformly charged, a device for forming the protective layer, a process cartridge using the device, and an image forming apparatus.
2. Description of the Related Art
In an electrophotographic process, an image is formed by subjecting a photoconductor, which is used as a latent image bearing member, to a charging step, a exposing step, a developing step, a transferring step.
Specifically, when a latent electrostatic image corresponding to image information has been formed after uniform charging of the photoconductor, the latent electrostatic image is made into a visible image with charged toner supplied from a developing device.
The visible image is transferred onto a transfer medium such as transfer paper, and subsequently made into an output image by being fixed on the transfer medium by means of fusing and penetrating actions obtained utilizing heat and pressure or solvent gas.
Developing devices are based upon either two-component developing methods using two-component developers in which toner is charged by agitating and mixing toner particles and carrier particles, or one-component developing methods using one-component developers in which charging is performed, for example, by frictional charging of toner itself without using carrier particles.
As already known, the one-component developing methods are classified into: magnetic one-component developing methods in which toner particles are held on development sleeves, which are used to supply developers, by magnetic force; and nonmagnetic one-component developing methods which do not utilize magnetic force.
The two-component developing methods are frequently used for copiers for which stable charge rising properties and chargeability of toner particles, and long-term stabilization of image quality are required, facsimile devices with copying functions, complex machines used with functions of printers and other functions combined together, etc., whereas the one-component developing methods are frequently used for compact printers and facsimile devices for which space saving and cost reduction are required.
Output images include not only single-color images such as monochrome images but also multicolor images such as full-color images, and demands for higher image quality have been increasing in recent years. Accordingly, in order to meet these demands, the quality of members used in image forming processes also needs to be maintained at a high level.
In each image forming apparatus, regardless of differences among the developing methods, while a photoconductor serving as an image bearing member for which a drum or belt is used is being moved by rotation or the like, the photoconductor is uniformly charged, a latent electrostatic image pattern is formed on the photoconductor by optical writing using a laser beam or the like, the latent electrostatic image pattern is visualized by a developing device, and the visible image is transferred onto a transfer medium so as to obtain an output image. Here, it should be noted that, in some cases, discharge products produced in the charging step and/or untransferred toner not transferred to the transfer medium are/is present on the photoconductor after the transfer of the visible image onto the transfer medium, or toner is attached to a background portion and thus present in positions not related to an image portion.
Accordingly, after the transferring step, the photoconductor is subjected to a cleaning step to remove the discharge products and/or the residual toner.
Among cleaning methods employed in the cleaning step, what is generally well known is a method of using a rubber blade which is inexpensive, has a simple structure and is superior in cleanability.
However, since the rubber blade removes residues present on the photoconductor surface by being pressed against the photoconductor surface, there is a great deal of stress caused by friction between the photoconductor surface and the rubber blade, and so the rubber blade is easily abraded. Additionally, as for an organic photoconductor used as a photoconductor against which a rubber blade is pressed, abrasion and scratches of photoconductor surface layer(s) arise, thereby shortening the lifetimes of the rubber blade and the organic photoconductor itself.
Moreover, in recent years, more and more toners used in image formation have been made smaller in particle size in response to demands for higher image quality.
In an image forming apparatus using a small particle size toner, the proportion of the toner leaking through a gap between a cleaning blade and the photoconductor surface is large; especially when the dimensional accuracy or attachment accuracy of the cleaning blade is inadequate, or the cleaning blade partially vibrates, leakage of the toner increases greatly. Thus, formation of a high-quality image is often hindered.
Thus, to lengthen the lifetime of an organic photoconductor and sustain high image quality over a long period of time, it is necessary to restrain deterioration of members, caused by friction, and thereby improve cleanability.
Conventional methods of reducing the friction include a method of forming a lubricant film on a photoconductor surface by supplying a lubricant onto the photoconductor surface and uniformly spreading the supplied lubricant with a cleaning blade.
As methods for forming lubricant films by supplying lubricant components, the following methods have been proposed.
There has been proposed a method of forming a lubricant film on a photoconductor surface by supplying the photoconductor surface with a solid lubricant composed mainly of zinc stearate (refer, for example, to Japanese Patent Application Publication (JP-B) No. 51-22380).
There has been proposed a method of maintaining lubricating performance by using a lubricant supply device that supplies a lubricant composed mainly of a higher alcohol having 20 to 70 carbon atoms, which allows the higher alcohol to stagnate on an end of a blade nip portion as particles that have no definite shape, and utilizing the appropriate wettability of the lubricant to the surface of an image bearing member (refer, for example, to Japanese Patent Application Laid-Open (JP-A) No. 2005-274737).
There has been proposed a method of sustaining smooth lubricating action over a long period of time by using powder of a specific alkylene bis alkyl acid amide compound as a lubricant component, which allows fine powder particles to be present on the interface between a cleaning blade and an image bearing member (refer, for example, to JP-A No. 2002-97483).
There has been proposed a method of reducing frictional force between an image bearing member and a cleaning member by supplying the photoconductor surface with lubricants prepared by adding inorganic lubricants to solid lubricants composed mainly of zinc stearate (refer, for example, to JP-A No. 2005-171107).
There has been proposed a method in which application of an image-bearing member protecting agent that contains a fatty acid metal salt and boron nitride makes it possible to maintain lubricating properties between a cleaning blade and an image bearing member by means of a lubricating effect of the boron nitride even under the influence of electric discharge performed in the vicinity of the image bearing member in a charging step, and leakage of toner is thereby prevented (refer, for example, to JP-A No. 2006-350240).